Heretofore, in a soldering process for bonding a semiconductor element or device to be used in a power module such as an IGBT (insulated gate bipolar transistor) element and others to a substrate through a solder, a hydrogen atmosphere is formed in a chamber serving as a process chamber and the process is conducted under reduced pressure of the atmosphere (for example, Patent Literature 1).
A typical hydrogen vacuum furnace has such a configuration as shown in FIG. 5. Specifically, a hydrogen vacuum heating furnace 90 includes a process chamber 1 in which a subject 10 to be heated (“subject”) will be placed or set, a heating chamber 2 in which heater lamps 25 serving as a heating source are housed, and a crystal board 3 for separating the process chamber 1 and the heating chamber 2. The process chamber 1 is provided with a feed port 11 for feeding hydrogen or a mixture gas of hydrogen and inert gas and an exhaust port 12 for discharging gas from the process chamber 1. In the hydrogen vacuum furnace 90, the subject 10 is heated by a radiant ray (an infrared ray or the like) from the heater lamp 25.
The hydrogen vacuum furnace having the above configuration that separates the heater lamps from the subject to be heated provides the following merits as compared with a configuration in which a heater lamp is placed in a process chamber:    (1) The heater lamp which becomes an ignition source is separated from hydrogen or a mixture gas of hydrogen and inert gas;    (2) The heater lamp is prevented from electrically discharging during heating under reduced pressure;    (3) The heater lamp can be replaced with another one without contaminating the inside of the process chamber (Easy maintenance);    (4) The volume of the process chamber is reduced (Reduced amount of gas to be used);    (5) Impurities (flux contained in solder or the like) are prevented from sticking to the heater lamp;    (6) The process chamber is prevented from contamination by impurities (a reflection film coated on the surface of the heater lamp or the like) from the heater lamp.    Patent Literature 1: JP2005-205418A